A Novel Approach to In Situ Coating Thickness Measurements in Thermal Spraying

Coating thickness is considered to be one of the most important characteristics of thermally sprayed coatings. Despite this, there is a lack of a measurement method that could evaluate in situ the coating thickness with a sufficient accuracy that could be used as a feedback signal for online, closed-loop control. Offline methods that produce spatially resolved coating thickness measurements by capturing the surface topography have already been demonstrated to provide results with a high accuracy, comparable to the standard reference microscopical measurement method. However, up to now, the approach has not been applied in situ. This paper presents a novel approach to in situ measure spatially resolved coating thickness. It is based on a differential distance measurement of sample thickness before and after applying the coating. A high-resolution 3D camera is used to capture the surface topography and include it in the thickness measurement. The technique provides a 3D view of the deposited coating thickness measured in situ and gives results with excellent accuracy when compared to the reference microscopical method.